Both Unreal Tournaments work natively in Linux, and a guy outside Epic (but evidently supported by them) tweaks patches to work with Linux.
Also, since id released the source code for quakeworld it is possible to run Quake native in Linux if you compile it right.
And from this with a little fudging you can make every game built on the original Quake engine or the first two Unreal engines run in Linux without emulation.
Also, WINE *almost* counts as an emulator now. It didn't when it was first released, because at the time it was basically a patch that corrected a tiny number of Win32 programs to talk with Linux. Since then the correction has been progressively generalised until now where it is practically an emulation of a Win32 API, but it still technically isn't as it does not mimic the entire thing yet - so it is still just a really, really generalised patch. For now.